Using electric mixer, beat sugar and eggs in medium bowl until very thick and pale, about 3 minutes. Stir in melted chocolate mixture and vanilla. Mix flour, baking powder and salt in another medium bowl. Stir into chocolate mixture. Mix in chocolate-covered raisins.

Pour batter into prepared pan. Bake until tester inserted into center comes out with a few moist crumbs attached and top cracks in places, about 30 minutes. Transfer to rack and cool in pan. (Can be made 1 day ahead. Cover with foil and let stand at room temperature.) Cut brownies into squares.